Author Topic: Centre stand (1965 B40F)  (Read 941 times)

0 Members and 1 Guest are viewing this topic.

JulianS

  • Empire Star
  • *****
  • Posts: 2404
  • A10
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #15 on: 24 April, 2022, 18:23:21 »
Another view.

Phil C

  • Golden Flash
  • *****
  • Posts: 1916
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #16 on: 24 April, 2022, 18:56:54 »
Yes, thanks Julian, clearly mine is at the wrong angle, so presumably there's wear at the top of the legs and/or the lugs on the frame. Hopefully it will be at the top of the legs, as that will probably be easier to fix than the lugs on the frame. I'll put the bike on its sidestand and look to (carefully, so the bike doesn't fall over!) remove the centre stand to have a good look at it.

Phil

Phil C

  • Golden Flash
  • *****
  • Posts: 1916
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #17 on: 24 April, 2022, 19:21:26 »
But actually, there must be a better way than having it on the side stand? Do I need to buy some kind of jack, so that I can see the centre stand's operation with it held up clear of the ground somehow?

Phil.

spaceman

  • Silver Star
  • ****
  • Posts: 395
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #18 on: 24 April, 2022, 19:53:33 »
The pic shows the top of a C15 stand with the front of the bike on the left. It is the sloping top edge in front of the hole that presses against the frame to stop the forward motion of the stand. As with this example, this edge gets hammered downwards causing the stand to tilt too far forward lowering the height of the bike. To repair, this edge needs to be built back up by welding on metal until the stand angel is correct again.

spaceman

  • Silver Star
  • ****
  • Posts: 395
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #19 on: 25 April, 2022, 07:57:00 »
Going from memory, the B40 frame is fitted with two round topped triangular shaped lugs on which the centre stand pivots. The inside half of the lugs is machined so that, above the top of the centre stand mounting arms, the machined parts of the frame lugs provide shallow V-shaped cut-outs. It is these cut-out shapes that limits the travel of the centre stand in both directions.

However, over time, both the V-shaped cut-outs and the triangular top of the centre stand legs will wear from the stand snapping open and closed and therefore the amount of travel will gradually increase. Even with a bare frame, I think it would be very difficult to repair the frame lugs. A replacement centre stand might cure the problem but this will depend on how much the frame lugs are worn. The alternative, as suggested, is to change the shape of the front part of the triangular tops on the centre stand by welding on some metal - a relatively easy job for a welder!


Phil C

  • Golden Flash
  • *****
  • Posts: 1916
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #20 on: 25 April, 2022, 08:59:05 »
Thanks very much, spaceman. I'll have a look at mine today - then it will probably be clearer to me how exactly it operates and what I can do to repair it. I'll report back.

Meanwhile, any thoughts on the jack/ lift issue?

Phil

spaceman

  • Silver Star
  • ****
  • Posts: 395
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #21 on: 25 April, 2022, 11:32:47 »
The pictures below show how the centre stand works - this is a C15 frame but will be identical to the B40.

The frame is basically flat between each pair of triangular brackets on the frame and it is this flat surface that limits the travel of the centre stand due to the ~ triangular shape at the top of each leg.

However, examining my example C15 frame, it looks as though most of the wear is probably in the centre stand pivot holes rather than in the bearing surfaces. Having dug this frame out, I will try to work out what angle the centre stand should deploy at and will then repair the centre stand to achieve it. First step, will be to re-bush the centre stand pivot holes to take out the free play and, if necessary, I will then re-profile the top of each leg with a bit of welding.

For the B40 in question, I would recommend taking off the centre stand to see what shape it is in and to see what needs to be done to restore it to the correct deployed geometry.

Pete C

  • Royal Star
  • ***
  • Posts: 234
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #22 on: 25 April, 2022, 12:44:32 »
+1 for Julian.
The stand should be almost vertical in use. Yours has a fair bit of wear on the mounting lugs, stops, etc and it does look like the feet have been added to to compensate so meaning you have to lift higher to get the bike on to the stand.
You neeed to remove the stand and find out where the wear is and after fixing that you can grind off the excess on the feet.

I had the same problem with my B31.

Pete C

  • Royal Star
  • ***
  • Posts: 234
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #23 on: 25 April, 2022, 12:46:25 »
sorry, I had only read the 1st page of comments before posting so didn't see that the topic had been answered  ::) ::)

Phil C

  • Golden Flash
  • *****
  • Posts: 1916
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #24 on: 25 April, 2022, 13:23:03 »
Thanks so far everyone. I'm taking the stand off the bike, which is pretty straightforward except one of the pins won't come out. Used wd40, drift punch, hammer, hot air gun, etc, but so far no joy. I'll get it out eventually and can then have a good look, think, and - crucially!  - discussion on this forum.
  Phil

Phil C

  • Golden Flash
  • *****
  • Posts: 1916
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #25 on: 25 April, 2022, 15:24:44 »
The centre stand is now off the bike. Going by what I can see, and from advice received on this forum, it appears what's needed now is:
1. Build up (with weld) the surface that acts as a stop. By how much I don't know, as I have the bike on its side stand rather than raised up, which would be ideal so that I could them offer the stand up at the correct angle and judge how much weld would be needed. I might need to use guesswork and trial and error. Any thoughts please? (I've no welding gear so might have to take it to my local friendly blacksmith.)

2.  Correct the elongated pivot holes. Basically they need bushing, so I'll have to ask the blacksmith to bore out the holes with a slot drill on a milling machine, turn up some bushes to fit, braze them in place, and finish the holes to size. Need to think about the position of the hole centres.

3. Cut off the extensions a previous owner appears to have welded onto the bottoms of the legs.

Any thoughts on any of the above would be appreciated. Thanks very much.

Phil



« Last Edit: 25 April, 2022, 15:27:44 by Phil C »

spaceman

  • Silver Star
  • ****
  • Posts: 395
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #26 on: 25 April, 2022, 16:38:10 »
I would recommend getting the pivot holes sorted first because you can't work out what re-profiling of the top surface needs to be done with that much free play in the pivot. I've had a close look at the C15 centre stand I've got and decided that the upper most part of the pivot hole is ok and the hole has been elongated downwards - if you take that into account, you can then see where the centre of the hole should be.

Once the pivot holes have been sorted and the extra feet removed from the centre stand, it can be re-fitted after which it should be relatively easy to work out what angle it needs to sit at and to also work out what thickness of metal needs to be added at the top of stand.

Phil C

  • Golden Flash
  • *****
  • Posts: 1916
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #27 on: 25 April, 2022, 17:27:34 »
When you say the uppermost part of the hole is okay, do you mean the bit nearest the vee, or the bit that is uppermost when the stand is folded up?  Phil

Phil C

  • Golden Flash
  • *****
  • Posts: 1916
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #28 on: 25 April, 2022, 18:05:28 »
Further to my question in my previous message, it occurs to me that there's not a huge amount of matuerial at the side of the hole for bushing (see photo). Either the wall of the bush on one side is going to be very thin, or the wall of the parent material will be very thin, or they'll both be pretty thin. And of course they will be brazed/welded there. Anyone bushed these things before? Phil
« Last Edit: 25 April, 2022, 18:07:15 by Phil C »

JulianS

  • Empire Star
  • *****
  • Posts: 2404
  • A10
    • View Profile
Re: Centre stand (1965 B40F)
« Reply #29 on: 25 April, 2022, 19:08:46 »
The alternative course of action is to use the bike with just the prop stand whilst  searching for a replacement centre stand - you might, in time,  find one which was in acceptable condition.